The present invention relates to devices and methods for measuring the color of objects, and more particularly to devices and methods for measuring the color of teeth, fabric or other objects or surfaces with a hand-held probe that presents minimal problems with height or angular dependencies.
Various color measuring devices such as spectrophotometers and colorimeters are known in the art. To understand the limitations of such conventional devices, it is helpful to understand certain principles relating to color. Without being bound by theory, Applicants provide the following discussion.
The color of an object determines the manner in which light is reflected from the surface of the object. When a light is incident upon an object, the reflected light will vary in intensity and wavelength dependent upon the color of the surface of the object. Thus, a red object will reflect red light with a greater intensity than a blue or a green object, and correspondingly a green object will reflect green light with a greater intensity than a red or blue object.
One method of quantifying the color of an object is to illuminate it with broad band spectrum or xe2x80x9cwhitexe2x80x9d light, and measure the spectral properties of the reflected light over the entire visible spectrum and compare the reflected spectrum with the incident light spectrum. Such instruments typically require a broad band spectrophotometer, which generally are expensive, bulky and relatively cumbersome to operate, thereby limiting the practical application of such instruments.
For certain applications, the broad band data provided by a spectrophotometer is unnecessary. For such applications, devices have been produced or proposed that quantify color in terms of a numerical value or relatively small set of values representative of the color of the object.
It is known that the color of an object can be represented by three values. For example, the color of an object can be represented by red, green and blue values, an intensity value and color difference values, by a CIE value, or by what are known as xe2x80x9ctristimulus valuesxe2x80x9d or numerous other orthogonal combinations. It is important that the three values be orthogonal; i.e., any combination of two elements in the set cannot be included in the third element.
One such method of quantifying the color of an object is to illuminate an object with broad band xe2x80x9cwhitexe2x80x9d light and measure the intensity of the reflected light after it has been passed through narrow band filters. Typically three filters (such as red, green and blue) are used to provide tristimulus light values representative of the color of the surface. Yet another method is to illuminate an object with three monochromatic light sources (such as red, green and blue) one at a time and then measure the intensity of the reflected light with a single light sensor. The three measurements are then converted to a tristimulus value representative of the color of the surface. Such color measurement techniques can be utilized to produce equivalent tristimulus values representative of the color of the surface. Generally, it does not matter if a xe2x80x9cwhitexe2x80x9d light source is used with a plurality of color sensors (or a continuum in the case of a spectrophotometer), or if a plurality of colored light sources are utilized with a single light sensor.
There are, however, difficulties with the conventional techniques. When light is incident upon a surface and reflected to a light receiver, the height of the light sensor and the angle of the sensor relative to the surface and to the light source also affect the intensity of the received light. Since the color determination is being made by measuring and quantifying the intensity of the received light for different colors, it is important that the height and angular dependency of the light receiver be eliminated or accounted for in some manner.
One method for eliminating the height and angular dependency of the light source and receiver is to provide a fixed mounting arrangement where the light source and receiver are stationary and the object is always positioned and measured at a preset height and angle. The fixed mounting arrangement greatly limits the applicability of such a method. Another method is to add mounting feet to the light source and receiver probe and to touch the object with the probe to maintain a constant height and angle. The feet in such an apparatus must be wide enough apart to insure that a constant angle (usually perpendicular) is maintained relative to the object. Such an apparatus tends to be very difficult to utilize on small objects or on objects that are hard to reach, and in general does not work satisfactorily in measuring objects with curved surfaces.
The use of color measuring devices in the field of dentistry has been proposed. In modern dentistry, the color of teeth typically are quantified by manually comparing a patient""s teeth with a set of xe2x80x9cshade guides.xe2x80x9d There are numerous shade guides available for dentists in order to properly select the desired color of dental prosthesis. Such shade guides have been utilized for decades and the color determination is made subjectively by the dentist by holding a set of shade guides next to a patient""s teeth and attempting to find the best match. Unfortunately, however, the best match often is affected by the ambient light color in the dental operatory and the surrounding color of the patient""s makeup or clothing and by the fatigue level of the dentist.
Similar subjective color quantification also is made in the paint industry by comparing the color of an object with a paint reference guide. There are numerous paint guides available in the industry and the color determination also often is affected by ambient light color, user fatigue and the color sensitivity of the user. Many individuals are color insensitive (color blind) to certain colors, further complicating color determination.
In general, color quantification is needed in many industries. Several, but certainly not all, applications include: dentistry (color of teeth); dermatology (color of skin lesions); interior decorating (color of paint, fabrics); the textile industry; automotive repair (matching paint colors); photography (color of reproductions, color reference of photographs to the object being photographed); printing and lithography; cosmetics (hair and skin color, makeup matching); and other applications in which it useful to measure color in an expedient and reliable manners.
With respect to such applications, however, the limitations of conventional color measuring techniques typically restrict the utility of such techniques. For example, the high cost and bulkiness of typical broad band spectrometers, and the fixed mounting arrangements or feet required to address the height and angular dependency, often limit the applicability of such conventional techniques.
Moreover, another limitation of such conventional methods and devices are that the resolution of the height and angular dependency problems typically require contact with the object being measured. In certain applications, it may be desirable to measure and quantify the color of an object with a small probe that does not require contact with the surface of the object. In certain applications, for example, hygienic considerations make such contact undesirable. In the other applications such as interior decorating, contact with the object can mar the surface (such as if the object is coated with wet paint) or otherwise cause undesirable effects.
In summary, there is a need for a low cost, hand-held probe of small size that can reliably measure and quantify the color of an object without requiring physical contact with the object, and also a need for methods based on such a device in the field of dentistry and other applications.
In accordance with the present invention, devices and methods are provided for measuring the color of objects, reliably and with minimal problems of height and angular dependence. A handheld probe is utilized in the present invention, with the handheld probe containing a number of fiber optics. Light is directed from one (or more) light source fiber optics towards the object to be measured, which in certain preferred embodiments is a central light source fiber optic (other light source arrangements also may be utilized). Light reflected from the object is detected by a number of light receiver fiber optics. Included in the light receiver fiber optics are a plurality of perimeter fiber optics. In certain preferred embodiments, three perimeter fiber optics are utilized in order to take measurements at a desired, and predetermined height and angle, thereby minimizing height and angular dependency problems found in conventional methods. In certain embodiments, the present invention also may measure translucence and fluorescence characteristics of the object being measured, as well as surface texture and/or other surface characteristics.
The present invention may include constituent elements of a broad band spectrophotometer, or, alternatively, may include constituent elements of a tristimulus type calorimeter. The present invention may employ a variety of color measuring devices in order to measure color in a practical, reliable and efficient manner, and in certain preferred embodiments includes a color filter array and a plurality of color sensors. A microprocessor is included for control and calculation purposes. A temperature sensor is included to measure temperature in order to detect abnormal conditions and/or to compensate for temperature effects of the filters or other components of the system. In addition, the present invention may include audio feedback to guide the operator in making color measurements, as well as one or more display devices for displaying control, status or other information.
With the present invention, color measurements may be made with a handheld probe in a practical and reliable manner, essentially free of height and angular dependency problems, without resorting to fixtures, feet or other undesirable mechanical arrangements for fixing the height and angle of the probe with respect to the object.
Accordingly, it is an object of the present invention to address limitations of conventional color measuring techniques.
It is another object of the present invention to provide a method and device useful in measuring the color of teeth, fabric or other objects or surfaces with a hand-held probe of practical size that does not require contact with the object or surface.
It is a further object of the present invention to provide a color measurement probe and method that does not require fixed position mechanical mounting, feet or other mechanical impediments.
It is yet another object of the present invention to provide a probe and method useful for measuring color that may be utilized with a probe simply placed near the surface to be measured.
It is a still further object of the present invention to provide a probe and method that are capable of determining translucency characteristics of the object being measured.
It is a further object of the present invention to provide a probe and method that are capable of determining surface texture characteristics of the object being measured.
It is a still further object of the present invention to provide a probe and method that are capable of determining fluorescence characteristics of the object being measured.
Finally, it is an object of the present invention to provide a probe and method that can measure the area of a small spot singulary, or that also can measure irregular shapes by moving the probe over an area and integrating the color of the entire area.